A number of the later generation high activity olefin polymerization catalysts are prepared by processes which result in extremely fine catalyst particles. The use of such fine catalyst particles in actual commercial polymerization has often led to various problems including the production of undesirable levels of fine polymer and undesired difficulties in handling the catalyst.
One approach that has been taken with many fine high activity olefin polymerization and catalysts has been the application of prepolymer to increase the size and/or integrity of the catalyst particles which are ultimately charged to the polymerization zone.
The use of prepolymer on the catalyst introduces its own separate problems. For example, it has been noted that the presence of the prepolymer can result in plugged feeding lines and feeding difficulties in mud pots which arise from the tendency of such prepolymerized catalysts to bridge in the restrictive openings of either mud pots or feed lines. These problems become particularly evident as the level of prepolymer on the catalyst is increased. The feeding of catalyst slurries can even be a problem for particulate olefin polymerization catalysts that have not been subjected to prepolymerization, for example particulate chromium-containing catalysts.
In the prior art, there have been disclosures of using various particulate diluents such as silica gel or inert polymer in combination with the particulate catalyst. The use of particulate diluents has been found to introduce additional unique problems. For example, and most often, the particulate diluents result in undesired dilutions of the ultimate polymer properties.
An object of the present invention is to provide an improved method for charging a slurry of particulate olefin polymerization catalyst to the reaction zone.
Another object of the present invention is to provide a process for polymerizing olefins with a particulate olefin polymerization catalyst and a particulate diluent which has a less adverse effect upon the properties of the ultimate polymer than diluents heretofore used.
Another object of the present invention is to provide a process for polymerizing olefins which allows one to use olefin polymerization catalysts containing much higher levels of prepolymer than have generally been used in the past.
Other aspects, objects, and advantages of the present invention will be apparent to those skilled in the art having the benefit of the following disclosure.